1. Field of the Invention
The present invention relates to heat exchange elements of the air-tube type for a heat exchanger unit; the heat exchange elements are connected via flexible connecting lines with the liquid supply and withdrawal channels, which are separated from the heat exchange elements. Together with the channels, the heat exchange elements are supported on a support structure having relatively large open support intervals. The heat exchange elements have a relatively short dimension, i.e. are not very wide, in the longitudinal direction of the tubes through which the air flows.
2. Description of the Prior Art
Heat exchange elements of the air-tube type have been known in theory for years as radiators in the automobile and aircraft industries, and also have even been used formerly to a certain extent. In such radiators, the ends of the otherwise round, light metal tubes are expanded into a multi-sided configuration, especially a hexagonal configuration, and are connected with one another in a leak proof manner in the region of the edges or side surfaces of the multi-sided configuration by means of hard soldering or the like. However, in practice such radiators have not been successfully used because the permanent sealing problems and corrosion problems could not be satisfactorily resolved; furthermore, the elements could not be economically produced.
In recent times, it has been proposed in publications to use heat exchange elements of the air-tube type in dry cooling towers. These air-tube-dry cooling elements, designated in this application as LRT-elements, for dry cooling towers, were optimized in that, with the exception of the tubes along the edges, the tube ends which were enlarged to the hexagonal configuration, and the presence of turbulancegenerating means, for example in the form of beads, transverse grooves, or the like, which are distributed over the active length of the tube, increased the heat transfer by the air. For economical reasons, an optimum tube length of between 0.6 m and 1 m, a tube thickness of from 0.4 to 0.5 mm, and a length of about 4 m and a width of about 3 m, which dimensions were determined by transportation conditions, were established.
The heretofore known LRT-elements have a boxshaped design (parallelepipidal, quadratic or squared shape) with planar walls. To facilitate removal of water and air, the elements were disposed at a slight incline. However, due to the weight of the liquid which flows around the tubes, and to the dead weight of the elements, tension forces resulted at the transition surfaces between the elements and the water supply and withdrawal channels; these tension forces had to be compensated for by expensive and complicated structural means. Furthermore, the expansion or deformation of the elements caused by temperature also had to be compensated for. If no specific structural measures, for example displaceability of the elements, are taken to compensate for this deformation, the latter leads to a downward deflection or bending of the elements, which have large, open support intervals. This bending, in turn, results in further tension forces at the transition surfaces to the water supply and withdrawal channels.
The previously unresolved permanent sealing and corrosion problems could be eliminated by selecting a suitable synthetic material in place of aluminum, brass, or a similar metal. However, the aforementioned drawbacks with regard to the occurrence of tension forces are particularly serious with LRT-elements of synthetic material because, as is well known, synthetic materials have a relatively great thermal expansion, for example 7 mm per m and 100.degree. C. temperature difference, and, in comparison to metals, have a significantly poorer strength and inherent rigidity.
An object of the present invention is to improve heat exchange elements of the aforementioned general type such that no tension forces occur at the transition surfaces between the LRT-elements and the walls of the channels which serve for supply and withdrawal of liquid.